Jacks with a fixed piston are known for handling, moving and manipulating workpieces. In this type of jack, the body of the jack moves in relation to the piston, and a guiding element is provided to ensure the longitudinal motion of the body and to prevent rotation between the piston and the body. Such a jack is also advantageously used in handlers and robots.
Patents FR 2 566 847 and FR 2 588 328 held by the applicant, describe a jack with a fixed piston, in which the body of the jack consists of a tube sliding on the fixed piston. A guiding element is also provided. The guiding element is installed parallel to the body of the jack and is held in place by blocks. The guiding element is connected to the body of the jack through a connecting piece of an appropriate shape. To reduce the overall dimensions, the guiding element remains inside the casing when the body of the jack moves outward.
The inconvenience of this type of jack is that the body of the jack is a tubular part, ill-adapted to form the arm of a robot and to be equipped with a tool because of its shape, and also because of its mechanical resistance. In addition, there are difficulties in manufacturing the body of the jack.
Further, the guiding of the body of the jack is bulky and its fabrication cost is high. While other known guiding systems might allow a shorter length, the width and height can still be substantial, i.e., in the traverse directions of the jack movement.
It can also be desirable to be able to stop the jack movement, before it reaches its end of travel. This stop should take place both on the occasion of an outward movement and during the return of the body of the jack.
Patent FR 2 588 328, mentioned above, describes a jack which makes it possible to obtain intermediate stops. For this purpose, the jack contains a reversible screw which is also used as the guiding element. The length of the screw is approximately equal to the total travel of the jack and is equipped with a blocking component to stop the rotation of the screw for a given travel of the body of the jack. The blocking component is activated by sensors or by a rotating coder. This device is electrical and its realization cost is high.
As shown in Patent EP-B-0 472 778, it is also known to stop the arm of a jack-activated handler during its movement by placing an adjustable limit stop in a "T" shaped groove of the handler arm. In this jack, the handler is provided with a double-effect jack controlling the movement of a shock absorber. The double-effect jack retracts to intercept the limit stop to stop movement of the handler arm. However, this device only allows a small adjustment range at the end of travel of the jack, and the stop can only occur when the rod moves outward. In addition, three shock absorbers are necessary: (i) one for the limit stop at the end of travel of the handler arm, (ii) one at the end of travel of the withdrawal, and (iii) one for the intermediate stop.
As such, it is believed there is a demand in the industry for an improved guided jack with fixed piston for handling, moving and manipulating workpieces.